This invention relates to the field of processing read-back signals representing data recorded on a storage media which are read using a transducer means and more particularly to a simplified circuit for data signal processing.
The use of an equalizer on the input signal from magnetic data storage devices affords a significant reduction in the soft error rate that can provide significant increase in storage capacity at a given tolerated error rate. This can result in an error rate improvement of 100 times or two orders of magnitude. This improvement, in conjunction with transducer head and media development, make possible the major portion of recent storage density improvements.
A feedforward equalizer consists of a passive network and a differential amplifier. The input signal to the passive network is "fed forward" and summed or differenced with a portion of the network output signal. The resulting signal is the equalized output. An early equalizer of this type is described in "An Improved Pulse Slimming Method For Magnetic Recording" by R. C. Schneider, IEEE Transactions on Magnetics, Sept. 1975, pp. 1240-1241.
The development of equalizer devices has included two stage devices in which each stage functioned to equalize both amplitude and phase. This intermixing of the functions results in adjustment complexity.
Equalizers have been improved by a circuit that uses two feed forward stages, but permits independent control of amplitude and phase (IBM Technical Disclosure Bulletin, Oct. 1977, pp. 1705-1706, "Time Domain Adjustable Equalizer by F. Castor and H. J. Gardner).
It has been shown that amplitude equalization can be accomplished using a single feedforward stage, if the passive network is a reflective delay line. This device has been called a cosine equalizer in the article "Improvement of Recording Density By Means of Cosine Equalizer" by T. Kameyama, S. Takanami and R. Arai, IEEE Transactions on Magnetics, Nov. 1976, pp. 746-748. Another solution is a four stage structure with two stages used for amplitude equalization and two stages for phase equalization, as shown in U.S. patent application Ser. No. 815,110 filed Dec. 31, 1985. Thus all feedforward equalizers which correct both amplitude and phase use a minimum of two stages while single stage equalizers have had the capability of equalizing for amplitude only.